simplify `Transition` by removing dead members (#94467)
Remove a number of functions from `Transition` that are never overridden
and had trivial implementations.
This reveals that the default `process_context` function is making a
copy of the module context simply without the `transition` (makes sense)
but also with the `replace_externals` property reset to `true`. It isn't
clear if that is intentional?
This is just a code health thing no real perf win expected (save a tiny
bit of code size)
